In the long march toward a more parliamentary and partisan Washington, National Journal’s 2010 congressional vote ratings mark a new peak of polarization.

For only the second time since 1982, when NJ began calculating the ratings in their current form, every Senate Democrat compiled a voting record more liberal than every Senate Republican—and every Senate Republican compiled a voting record more conservative than every Senate Democrat. Even Nebraska’s Ben Nelson, the most conservative Democrat in the rankings, produced an overall voting record slightly to the left of the most moderate Republicans last year: Ohio’s George Voinovich and Maine’s Susan Collins and Olympia Snowe. The Senate had been that divided only once before, in 1999.

But the overall level of congressional polarization last year was the highest the index has recorded, because the House was much more divided in 2010 than it was in 1999. Back then, more than half of the chamber’s members compiled voting records between the most liberal Republican and the most conservative Democrat. In 2010, however, the overlap between the parties in the House was less than in any previous index.

Just five House Republicans in 2010 generated vote ratings more liberal than the most conservative House Democrat, Gene Taylor of Mississippi. Just four Democrats produced ratings more conservative than the most liberal Republican, Joseph Cao of Louisiana. Every other House Republican produced a more conservative vote rating than every other House Democrat, even though a substantial number of those Democrats pursued a relatively moderate course overall. Of the nine members who were outliers last year, only one—Republican Walter Jones of North Carolina—is still in Congress. That makes him the only lawmaker in the House or Senate this year to have a 2010 vote rating out of sync with his party.

The results document another leap forward in the fusion of ideology and partisanship that has remade Congress over the past three decades, the period tracked by NJ’s vote ratings. For most of American history, the two parties operated as ramshackle coalitions that harbored diverse and even antithetical views. Each party’s Senate caucus housed ideological antagonists, such as progressive Democratic titan Hubert Humphrey of Minnesota and segregationist stalwart Richard Russell of Georgia, or New Right Republican firebrand Jesse Helms of North Carolina and silk-stocking New York City liberal Jacob Javits. Such contrasts are not extinct. But since the early 1980s, they have vastly diminished as the differences within each party have narrowed and the distance between them has widened.

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Over that period, “it’s just a straight, linear increase” in congressional polarization, says Gary Jacobson, a University of California (San Diego) political scientist who specializes in Congress. “There’s a little bit of bumping around in the numbers here and there, but the basic movement is toward the parties moving further and further apart. The 1970s are a high point of all the cross-party [coalitions]. The last three decades are ones of pulling apart.”

In 2010, the vote ratings show, the ideological consolidation was greater among Republicans than Democrats. Almost without exception House Republicans generated strongly conservative voting records, regardless of the demography or political leanings of their districts. By contrast, House Democrats from districts that voted for John McCain in 2008 or are dominated by working-class whites produced much less liberal records than their colleagues from districts that strongly supported Barack Obama or are more racially diverse and well educated. In the Senate, just eight Republicans notched a composite conservative score of less than 70, while 21 Democrats received a liberal ranking of less than 70.

The results capture the continued remaking of Congress into an institution defined by much greater partisan discipline and philosophical conformity. Occasionally, legislators can still build idiosyncratic coalitions across party lines, as occurred during some of the votes on the free-wheeling House debate over spending earlier this month. Likewise, a bipartisan group of senators is attempting to build a cross-party alliance to advance the recommendations of President Obama’s debt-reduction commission.

But increasingly, on the biggest issues, the parties line up in virtual lockstep against each other, as they did on many of the key measures in the 2010 rankings, such as the Senate votes on health care and financial-services reform. (Even on the House’s final vote last weekend on funding the government through September, every Democrat voted in opposition and all but three Republicans voted in support.) All of this is fundamentally changing the way Congress gets things done—when it gets things done at all. “If you are the whip in either party you are liking this, [because] it makes your job easier,” says Mississippi Republican Trent Lott, the former Senate majority leader (and before that the GOP Senate whip). “In terms of getting things done for the country, that’s not the case.”